1. 10 Dec, 2006 1 commit
    • mnislaih's avatar
      Playing with closures · 2c92736e
      mnislaih authored
      RtClosureInspect includes a bunch of stuff for playing with closures:
      
      - the datatype Closure is the low level representation type
      - the datatype Term is the high level representation type
      - cvObtainTerm is the main entry point, providing the Term representation of an arbitrary closure
      2c92736e
  2. 16 Oct, 2006 1 commit
  3. 11 Oct, 2006 2 commits
    • Simon Marlow's avatar
      ab22f4e6
    • Simon Marlow's avatar
      Interface file optimisation and removal of nameParent · b00b5bc0
      Simon Marlow authored
      This large commit combines several interrelated changes:
      
        - IfaceSyn now contains actual Names rather than the special
          IfaceExtName type.  The binary interface file contains
          a symbol table of Names, where each entry is a (package,
          ModuleName, OccName) triple.  Names in the IfaceSyn point
          to entries in the symbol table.
      
          This reduces the size of interface files, which should
          hopefully improve performance (not measured yet).
      
          The toIfaceXXX functions now do not need to pass around
          a function from Name -> IfaceExtName, which makes that
          code simpler.
      
        - Names now do not point directly to their parents, and the
          nameParent operation has gone away.  It turned out to be hard to
          keep this information consistent in practice, and the parent info
          was only valid in some Names.  Instead we made the following
          changes:
      
          * ImportAvails contains a new field 
                imp_parent :: NameEnv AvailInfo
            which gives the family info for any Name in scope, and
            is used by the renamer when renaming export lists, amongst
            other things.  This info is thrown away after renaming.
      
          * The mi_ver_fn field of ModIface now maps to
            (OccName,Version) instead of just Version, where the
            OccName is the parent name.  This mapping is used when
            constructing the usage info for dependent modules.
            There may be entries in mi_ver_fn for things that are not in
            scope, whereas imp_parent only deals with in-scope things.
      
          * The md_exports field of ModDetails now contains
            [AvailInfo] rather than NameSet.  This gives us
            family info for the exported names of a module.
      
      Also:
      
         - ifaceDeclSubBinders moved to IfaceSyn (seems like the
           right place for it).
      
         - heavily refactored renaming of import/export lists.
      
         - Unfortunately external core is now broken, as it relied on
           IfaceSyn.  It requires some attention.
      b00b5bc0
  4. 06 Oct, 2006 1 commit
  5. 05 Oct, 2006 1 commit
  6. 28 Sep, 2006 1 commit
  7. 20 Sep, 2006 1 commit
    • chak@cse.unsw.edu.au.'s avatar
      Extended TyCon and friends to represent family declarations · e8a591c1
      chak@cse.unsw.edu.au. authored
      Mon Sep 18 18:50:35 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
        * Extended TyCon and friends to represent family declarations
        Tue Aug 15 16:52:31 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
          * Extended TyCon and friends to represent family declarations
      e8a591c1
  8. 19 Sep, 2006 1 commit
    • Simon Marlow's avatar
      Packages cleanup, and allow new packages to be loaded with :set again · ee565d46
      Simon Marlow authored
      This cleans up the package subsystem a little.  There are some
      changes to the GHC API as a result.
      
        - GHC.init and GHC.initFromArgs are no longer necessary.
      
        - GHC.newSession takes the root of the GHC tree as an argument
          (previously passed to GHC.init).
      
        - You *must* do GHC.setSessionDynFlags after GHC.newSession,
          this is what loads the package database.
      
        - Several global vars removed from SysTools
      
        - The :set command in GHCi can now cause new packages to be loaded,
          or can hide/ignore existing packages.
      ee565d46
  9. 23 Aug, 2006 1 commit
  10. 22 Aug, 2006 1 commit
  11. 11 Aug, 2006 1 commit
  12. 10 Jul, 2006 1 commit
  13. 09 Jul, 2006 1 commit
  14. 25 Jul, 2006 1 commit
    • Simon Marlow's avatar
      Generalise Package Support · 61d2625a
      Simon Marlow authored
      This patch pushes through one fundamental change: a module is now
      identified by the pair of its package and module name, whereas
      previously it was identified by its module name alone.  This means
      that now a program can contain multiple modules with the same name, as
      long as they belong to different packages.
      
      This is a language change - the Haskell report says nothing about
      packages, but it is now necessary to understand packages in order to
      understand GHC's module system.  For example, a type T from module M
      in package P is different from a type T from module M in package Q.
      Previously this wasn't an issue because there could only be a single
      module M in the program.
      
      The "module restriction" on combining packages has therefore been
      lifted, and a program can contain multiple versions of the same
      package.
      
      Note that none of the proposed syntax changes have yet been
      implemented, but the architecture is geared towards supporting import
      declarations qualified by package name, and that is probably the next
      step.
      
      It is now necessary to specify the package name when compiling a
      package, using the -package-name flag (which has been un-deprecated).
      Fortunately Cabal still uses -package-name.
      
      Certain packages are "wired in".  Currently the wired-in packages are:
      base, haskell98, template-haskell and rts, and are always referred to
      by these versionless names.  Other packages are referred to with full
      package IDs (eg. "network-1.0").  This is because the compiler needs
      to refer to entities in the wired-in packages, and we didn't want to
      bake the version of these packages into the comiler.  It's conceivable
      that someone might want to upgrade the base package independently of
      GHC.
      
      Internal changes:
      
        - There are two module-related types:
      
              ModuleName      just a FastString, the name of a module
              Module          a pair of a PackageId and ModuleName
      
          A mapping from ModuleName can be a UniqFM, but a mapping from Module
          must be a FiniteMap (we provide it as ModuleEnv).
      
        - The "HomeModules" type that was passed around the compiler is now
          gone, replaced in most cases by the current package name which is
          contained in DynFlags.  We can tell whether a Module comes from the
          current package by comparing its package name against the current
          package.
      
        - While I was here, I changed PrintUnqual to be a little more useful:
          it now returns the ModuleName that the identifier should be qualified
          with according to the current scope, rather than its original
          module.  Also, PrintUnqual tells whether to qualify module names with
          package names (currently unused).
      
      Docs to follow.
      61d2625a
  15. 12 Jun, 2006 1 commit
  16. 18 Apr, 2006 1 commit
  17. 07 Apr, 2006 1 commit
    • Simon Marlow's avatar
      Reorganisation of the source tree · 0065d5ab
      Simon Marlow authored
      Most of the other users of the fptools build system have migrated to
      Cabal, and with the move to darcs we can now flatten the source tree
      without losing history, so here goes.
      
      The main change is that the ghc/ subdir is gone, and most of what it
      contained is now at the top level.  The build system now makes no
      pretense at being multi-project, it is just the GHC build system.
      
      No doubt this will break many things, and there will be a period of
      instability while we fix the dependencies.  A straightforward build
      should work, but I haven't yet fixed binary/source distributions.
      Changes to the Building Guide will follow, too.
      0065d5ab
  18. 06 Apr, 2006 1 commit
  19. 12 Mar, 2006 1 commit
  20. 10 Mar, 2006 1 commit
    • David Himmelstrup's avatar
      Parse OPTIONS properly and cache the result. · d700953c
      David Himmelstrup authored
      Use the lexer to parse OPTIONS, LANGUAGE and INCLUDE pragmas.
      This gives us greater flexibility and far better error
      messages. However, I had to make a few quirks:
        * The token parser is written manually since Happy doesn't
          like lexer errors (we need to extract options before the
          buffer is passed through 'cpp'). Still better than
          manually parsing a String, though.
        * The StringBuffer API has been extended so files can be
          read in blocks.
      I also made a new field in ModSummary called ms_hspp_opts
      which stores the updated DynFlags. Oh, and I took the liberty
      of moving 'getImports' into HeaderInfo together with
      'getOptions'.
      d700953c
  21. 04 Mar, 2006 1 commit
  22. 02 Mar, 2006 1 commit
  23. 26 Feb, 2006 1 commit
  24. 24 Feb, 2006 1 commit
  25. 10 Feb, 2006 1 commit
  26. 06 Feb, 2006 1 commit
    • Simon Marlow's avatar
      Basic completion in GHCi · 315a1f6c
      Simon Marlow authored
      This patch adds completion support to GHCi when readline is being
      used.  Completion of identifiers (in scope only, but including
      qualified identifiers) in expressions is provided.  Also, completion
      of commands (:cmd), and special completion for certain commands
      (eg. module names for the :module command) are also provided.
      315a1f6c
  27. 25 Jan, 2006 1 commit
    • simonpj@microsoft.com's avatar
      Simon's big boxy-type commit · ac10f840
      simonpj@microsoft.com authored
      This very large commit adds impredicativity to GHC, plus
      numerous other small things.
        
      *** WARNING: I have compiled all the libraries, and
      ***	     a stage-2 compiler, and everything seems
      ***	     fine.  But don't grab this patch if you 
      ***	     can't tolerate a hiccup if something is
      ***	     broken.
        
      The big picture is this:
      
      a) GHC handles impredicative polymorphism, as described in the
         "Boxy types: type inference for higher-rank types and
         impredicativity" paper
      
      b) GHC handles GADTs in the new simplified (and very sligtly less
         epxrssive) way described in the
         "Simple unification-based type inference for GADTs" paper
      
        
      But there are lots of smaller changes, and since it was pre-Darcs
      they are not individually recorded.
        
      Some things to watch out for:
        
      c)   The story on lexically-scoped type variables has changed, as per
           my email.  I append the story below for completeness, but I 
           am still not happy with it, and it may change again.  In particular,
           the new story does not allow a pattern-bound scoped type variable
           to be wobbly, so (\(x::[a]) -> ...) is usually rejected.  This is
           more restrictive than before, and we might loosen up again.
        
      d)   A consequence of adding impredicativity is that GHC is a bit less
           gung ho about converting automatically between
        	(ty1 -> forall a. ty2)    and    (forall a. ty1 -> ty2)
           In particular, you may need to eta-expand some functions to make
           typechecking work again.
         
           Furthermore, functions are now invariant in their argument types,
           rather than being contravariant.  Again, the main consequence is
           that you may occasionally need to eta-expand function arguments when
           using higher-rank polymorphism.
        
      
      Please test, and let me know of any hiccups
      
      
      Scoped type variables in GHC
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      	January 2006
      
      0) Terminology.
         
         A *pattern binding* is of the form
      	pat = rhs
      
         A *function binding* is of the form
      	f pat1 .. patn = rhs
      
         A binding of the formm
      	var = rhs
         is treated as a (degenerate) *function binding*.
      
      
         A *declaration type signature* is a separate type signature for a
         let-bound or where-bound variable:
      	f :: Int -> Int
      
         A *pattern type signature* is a signature in a pattern: 
      	\(x::a) -> x
      	f (x::a) = x
      
         A *result type signature* is a signature on the result of a
         function definition:
      	f :: forall a. [a] -> a
      	head (x:xs) :: a = x
      
         The form
      	x :: a = rhs
         is treated as a (degnerate) function binding with a result
         type signature, not as a pattern binding.
      
      1) The main invariants:
      
           A) A lexically-scoped type variable always names a (rigid)
       	type variable (not an arbitrary type).  THIS IS A CHANGE.
              Previously, a scoped type variable named an arbitrary *type*.
      
           B) A type signature always describes a rigid type (since
      	its free (scoped) type variables name rigid type variables).
      	This is also a change, a consequence of (A).
      
           C) Distinct lexically-scoped type variables name distinct
      	rigid type variables.  This choice is open; 
      
      2) Scoping
      
      2(a) If a declaration type signature has an explicit forall, those type
         variables are brought into scope in the right hand side of the 
         corresponding binding (plus, for function bindings, the patterns on
         the LHS).  
      	f :: forall a. a -> [a]
      	f (x::a) = [x :: a, x]
         Both occurences of 'a' in the second line are bound by 
         the 'forall a' in the first line
      
         A declaration type signature *without* an explicit top-level forall
         is implicitly quantified over all the type variables that are
         mentioned in the type but not already in scope.  GHC's current
         rule is that this implicit quantification does *not* bring into scope
         any new scoped type variables.
      	f :: a -> a
      	f x = ...('a' is not in scope here)...
         This gives compatibility with Haskell 98
      
      2(b) A pattern type signature implicitly brings into scope any type
         variables mentioned in the type that are not already into scope.
         These are called *pattern-bound type variables*.
      	g :: a -> a -> [a]
      	g (x::a) (y::a) = [y :: a, x]
         The pattern type signature (x::a) brings 'a' into scope.
         The 'a' in the pattern (y::a) is bound, as is the occurrence on 
         the RHS.  
      
         A pattern type siganture is the only way you can bring existentials 
         into scope.
      	data T where
      	  MkT :: forall a. a -> (a->Int) -> T
      
      	f x = case x of
      		MkT (x::a) f -> f (x::a)
      
      2a) QUESTION
      	class C a where
      	  op :: forall b. b->a->a
      
      	instance C (T p q) where
      	  op = <rhs>
          Clearly p,q are in scope in <rhs>, but is 'b'?  Not at the moment.
          Nor can you add a type signature for op in the instance decl.
          You'd have to say this:
      	instance C (T p q) where
      	  op = let op' :: forall b. ...
      	           op' = <rhs>
      	       in op'
      
      3) A pattern-bound type variable is allowed only if the pattern's
         expected type is rigid.  Otherwise we don't know exactly *which*
         skolem the scoped type variable should be bound to, and that means
         we can't do GADT refinement.  This is invariant (A), and it is a 
         big change from the current situation.
      
      	f (x::a) = x	-- NO; pattern type is wobbly
      	
      	g1 :: b -> b
      	g1 (x::b) = x	-- YES, because the pattern type is rigid
      
      	g2 :: b -> b
      	g2 (x::c) = x	-- YES, same reason
      
      	h :: forall b. b -> b
      	h (x::b) = x	-- YES, but the inner b is bound
      
      	k :: forall b. b -> b
      	k (x::c) = x	-- NO, it can't be both b and c
      
      3a) You cannot give different names for the same type variable in the same scope
          (Invariant (C)):
      
      	f1 :: p -> p -> p		-- NO; because 'a' and 'b' would be
      	f1 (x::a) (y::b) = (x::a)	--     bound to the same type variable
      
      	f2 :: p -> p -> p		-- OK; 'a' is bound to the type variable
      	f2 (x::a) (y::a) = (x::a)	--     over which f2 is quantified
      					-- NB: 'p' is not lexically scoped
      
      	f3 :: forall p. p -> p -> p	-- NO: 'p' is now scoped, and is bound to
      	f3 (x::a) (y::a) = (x::a)	--     to the same type varialble as 'a'
      
      	f4 :: forall p. p -> p -> p	-- OK: 'p' is now scoped, and its occurences
      	f4 (x::p) (y::p) = (x::p)	--     in the patterns are bound by the forall
      
      
      3b) You can give a different name to the same type variable in different
          disjoint scopes, just as you can (if you want) give diferent names to 
          the same value parameter
      
      	g :: a -> Bool -> Maybe a
      	g (x::p) True  = Just x  :: Maybe p
      	g (y::q) False = Nothing :: Maybe q
      
      3c) Scoped type variables respect alpha renaming. For example, 
          function f2 from (3a) above could also be written:
      	f2' :: p -> p -> p
      	f2' (x::b) (y::b) = x::b
         where the scoped type variable is called 'b' instead of 'a'.
      
      
      4) Result type signatures obey the same rules as pattern types signatures.
         In particular, they can bind a type variable only if the result type is rigid
      
      	f x :: a = x	-- NO
      
      	g :: b -> b
      	g x :: b = x	-- YES; binds b in rhs
      
      5) A *pattern type signature* in a *pattern binding* cannot bind a 
         scoped type variable
      
      	(x::a, y) = ...		-- Legal only if 'a' is already in scope
      
         Reason: in type checking, the "expected type" of the LHS pattern is
         always wobbly, so we can't bind a rigid type variable.  (The exception
         would be for an existential type variable, but existentials are not
         allowed in pattern bindings either.)
       
         Even this is illegal
      	f :: forall a. a -> a
      	f x = let ((y::b)::a, z) = ... 
      	      in 
         Here it looks as if 'b' might get a rigid binding; but you can't bind
         it to the same skolem as a.
      
      6) Explicitly-forall'd type variables in the *declaration type signature(s)*
         for a *pattern binding* do not scope AT ALL.
      
      	x :: forall a. a->a	  -- NO; the forall a does 
      	Just (x::a->a) = Just id  --     not scope at all
      
      	y :: forall a. a->a
      	Just y = Just (id :: a->a)  -- NO; same reason
      
         THIS IS A CHANGE, but one I bet that very few people will notice.
         Here's why:
      
      	strange :: forall b. (b->b,b->b)
      	strange = (id,id)
      
      	x1 :: forall a. a->a
      	y1 :: forall b. b->b
      	(x1,y1) = strange
      
          This is legal Haskell 98 (modulo the forall). If both 'a' and 'b'
          both scoped over the RHS, they'd get unified and so cannot stand
          for distinct type variables. One could *imagine* allowing this:
         
      	x2 :: forall a. a->a
      	y2 :: forall a. a->a
      	(x2,y2) = strange
      
          using the very same type variable 'a' in both signatures, so that
          a single 'a' scopes over the RHS.  That seems defensible, but odd,
          because though there are two type signatures, they introduce just
          *one* scoped type variable, a.
      
      7) Possible extension.  We might consider allowing
      	\(x :: [ _ ]) -> <expr>
          where "_" is a wild card, to mean "x has type list of something", without
          naming the something.
      ac10f840
  28. 18 Jan, 2006 1 commit
  29. 12 Jan, 2006 1 commit
    • simonmar's avatar
      [project @ 2006-01-12 16:16:28 by simonmar] · 44713ec1
      simonmar authored
      GHC.runStmt: run the statement in a new thread to insulate the
      environment from bad things that the user code might do, such as fork
      a thread to send an exception back at a later time.  In order to do
      this, we had to keep track of which thread the ^C exception should go
      to in a global variable.
      
      Also, bullet-proof the top-level exception handler in GHCi a bit;
      there was a small window where an exception could get through, so if
      you lean on ^C for a while then press enter you could cause GHCi to
      exit.
      44713ec1
  30. 06 Jan, 2006 1 commit
    • simonmar's avatar
      [project @ 2006-01-06 16:30:17 by simonmar] · 9d7da331
      simonmar authored
      Add support for UTF-8 source files
      
      GHC finally has support for full Unicode in source files.  Source
      files are now assumed to be UTF-8 encoded, and the full range of
      Unicode characters can be used, with classifications recognised using
      the implementation from Data.Char.  This incedentally means that only
      the stage2 compiler will recognise Unicode in source files, because I
      was too lazy to port the unicode classifier code into libcompat.
      
      Additionally, the following synonyms for keywords are now recognised:
      
        forall symbol 	(U+2200)	forall
        right arrow   	(U+2192)	->
        left arrow   		(U+2190)	<-
        horizontal ellipsis 	(U+22EF)	..
      
      there are probably more things we could add here.
      
      This will break some source files if Latin-1 characters are being used.
      In most cases this should result in a UTF-8 decoding error.  Later on
      if we want to support more encodings (perhaps with a pragma to specify
      the encoding), I plan to do it by recoding into UTF-8 before parsing.
      
      Internally, there were some pretty big changes:
      
        - FastStrings are now stored in UTF-8
      
        - Z-encoding has been moved right to the back end.  Previously we
          used to Z-encode every identifier on the way in for simplicity,
          and only decode when we needed to show something to the user.
          Instead, we now keep every string in its UTF-8 encoding, and
          Z-encode right before printing it out.  To avoid Z-encoding the
          same string multiple times, the Z-encoding is cached inside the
          FastString the first time it is requested.
      
          This speeds up the compiler - I've measured some definite
          improvement in parsing at least, and I expect compilations overall
          to be faster too.  It also cleans up a lot of cruft from the
          OccName interface.  Z-encoding is nicely hidden inside the
          Outputable instance for Names & OccNames now.
      
        - StringBuffers are UTF-8 too, and are now represented as
          ForeignPtrs.
      
        - I've put together some test cases, not by any means exhaustive,
          but there are some interesting UTF-8 decoding error cases that
          aren't obvious.  Also, take a look at unicode001.hs for a demo.
      9d7da331
  31. 03 Jan, 2006 1 commit
  32. 19 Dec, 2005 1 commit
  33. 30 Oct, 2005 1 commit
    • krasimir's avatar
      [project @ 2005-10-30 19:12:31 by krasimir] · 6e64c691
      krasimir authored
      Change the way in which the .exe suffix to the output file is added. The reason
      is that "-o main" will generate main.exe on Windows while the doesFileExists "main"
      in DriverPipeline.link will return False.
      6e64c691
  34. 29 Oct, 2005 1 commit
    • krasimir's avatar
      [project @ 2005-10-29 18:13:52 by krasimir] · 57d26da8
      krasimir authored
      The guessed output file should have ".exe" extension on Windows. ld tends to
      add .exe automatically if the output file doesn't have extension but if
      we don't add the extension explicitly then the doesFileExists check in
      DriverPipeline.link will fail.
      57d26da8
  35. 28 Oct, 2005 1 commit
    • simonmar's avatar
      [project @ 2005-10-28 11:35:35 by simonmar] · 55495951
      simonmar authored
      Change the default executable name to match the basename of the source
      file containing the Main module (or the module specified by -main-is),
      if there is one.  On Windows, the .exe extension is added.
      
      As requested on the ghc-users list, and as implemented by Tomasz
      Zielonka <tomasz.zielonka at gmail.com>, with modifications by me.
      
      I changed the type of the mainModIs field of DynFlags from Maybe
      String to Module, which removed some duplicate code.
      55495951
  36. 25 Oct, 2005 1 commit
    • simonmar's avatar
      [project @ 2005-10-25 12:48:35 by simonmar] · 78b72ed1
      simonmar authored
      Two changes from Krasimir Angelov, which were required for Visual
      Haskell:
      
        - messaging cleanup throughout the compiler.  DynFlags has a new
          field:
      
          log_action :: Severity -> SrcSpan -> PprStyle -> Message -> IO ()
      
          this action is invoked for every message generated by the
          compiler.  This means a client of the GHC API can direct messages to
          any destination, or collect them up in an IORef for later
          perusal.
      
          This replaces previous hacks to redirect messages in the GHC API
          (hence some changes to function types in GHC.hs).
      
        - The JustTypecheck mode of GHC now does what it says.  It doesn't
          run any of the compiler passes beyond the typechecker for each module,
          but does generate the ModIface in order that further modules can be
          typechecked.
      
      And one change from me:
      
        - implement the LANGUAGE pragma, finally
      78b72ed1
  37. 18 Aug, 2005 1 commit
    • krasimir's avatar
      [project @ 2005-08-18 20:32:46 by krasimir] · e0963b10
      krasimir authored
      add pprInstanceHdr function. It is analogous to pprTyThingHdr and prints the
      instance but without the "-- Defined at ...." comment. The function is used in
      VStudio to populate the ClassView tree.
      e0963b10
  38. 28 Jul, 2005 1 commit
    • simonpj's avatar
      [project @ 2005-07-28 14:58:27 by simonpj] · 721d0619
      simonpj authored
      Make ghc -M work when you give multiple files with the same
      module name.  We want to do this to the STABLE branch too,
      but this commit will not merge; it'll need to be done
      afresh.
      721d0619
  39. 19 Jul, 2005 1 commit
    • simonpj's avatar
      [project @ 2005-07-19 16:44:50 by simonpj] · a7ecdf96
      simonpj authored
      WARNING: this is a big commit.  You might want 
      	to wait a few days before updating, in case I've 
      	broken something.
      
      	However, if any of the changes are what you wanted,
      	please check it out and test!
      
      This commit does three main things:
      
      1. A re-organisation of the way that GHC handles bindings in HsSyn.
         This has been a bit of a mess for quite a while.  The key new
         types are
      
      	-- Bindings for a let or where clause
      	data HsLocalBinds id
      	  = HsValBinds (HsValBinds id)
      	  | HsIPBinds  (HsIPBinds id)
      	  | EmptyLocalBinds
      
      	-- Value bindings (not implicit parameters)
      	data HsValBinds id
      	  = ValBindsIn  -- Before typechecking
      		(LHsBinds id) [LSig id]	-- Not dependency analysed
      					-- Recursive by default
      
      	  | ValBindsOut	-- After typechecking
      		[(RecFlag, LHsBinds id)]-- Dependency analysed
      
      2. Implement Mark Jones's idea of increasing polymoprhism
         by using type signatures to cut the strongly-connected components
         of a recursive group.  As a consequence, GHC no longer insists
         on the contexts of the type signatures of a recursive group
         being identical.
      
         This drove a significant change: the renamer no longer does dependency
         analysis.  Instead, it attaches a free-variable set to each binding,
         so that the type checker can do the dep anal.  Reason: the typechecker
         needs to do *two* analyses:
      	one to find the true mutually-recursive groups
      		(which we need so we can build the right CoreSyn)
      	one to find the groups in which to typecheck, taking
      		account of type signatures
      
      3. Implement non-ground SPECIALISE pragmas, as promised, and as
         requested by Remi and Ross.  Certainly, this should fix the 
         current problem with GHC, namely that if you have
      	g :: Eq a => a -> b -> b
         then you can now specialise thus
      	SPECIALISE g :: Int -> b -> b
          (This didn't use to work.)
      
         However, it goes further than that.  For example:
      	f :: (Eq a, Ix b) => a -> b -> b
         then you can make a partial specialisation
      	SPECIALISE f :: (Eq a) => a -> Int -> Int
      
          In principle, you can specialise f to *any* type that is
          "less polymorphic" (in the sense of subsumption) than f's 
          actual type.  Such as
      	SPECIALISE f :: Eq a => [a] -> Int -> Int
          But I haven't tested that.
      
          I implemented this by doing the specialisation in the typechecker
          and desugarer, rather than leaving around the strange SpecPragmaIds,
          for the specialiser to find.  Indeed, SpecPragmaIds have vanished 
          altogether (hooray).
      
          Pragmas in general are handled more tidily.  There's a new
          data type HsBinds.Prag, which lives in an AbsBinds, and carries
          pragma info from the typechecker to the desugarer.
      
      
      Smaller things
      
      - The loop in the renamer goes via RnExpr, instead of RnSource.
        (That makes it more like the type checker.)
      
      - I fixed the thing that was causing 'check_tc' warnings to be 
        emitted.
      a7ecdf96